System.ByteOrder

This module offers an interface to portably work with byte arrays whose contents are known to be of a fixed endianness. There are two ways to use this module:

• Untyped Conversions: The functions toBigEndian, toLittleEndian, fromBigEndian, and fromLittleEndian convert between native-endian words and big/little-endian words. The word resulting from to(Big|Little)Endian should be written to a primitive byte array or a pointer afterwards. (There is no other purpose of such a conversion.) Similarly, the argument to from(Big|Little)Endian should be a word that was read from a primitive byte array or a pointer. This interface is useful when serializing or deserializing a data structure with fields of varying sizes.
• Typed Conversions: The type Fixed provides a convenient type-directed interface to working with arrays of homogenous words. This interface is easier to use and should be preferred when possible.

Suppose there is a protocol for aggregating numbers that uses stream sockets for communication. The protocol interprets all numbers as unsigned. It is described as follows:

1. The client sends the server a little-endian 16-bit number N. This is the count of numbers that will follow.
2. The client sends the server N little-endian 64-bit numbers.
3. The server responds with two 64-bit numbers: the sum and the product.

Assume the existence of a send and receive that block until the total number of requested bytes have been handled. Additionally, assume a typed and untyped function that convert between PrimArray and ByteArray by changing out the data constructor.

send :: Socket -> ByteArray -> IO ()
receive :: Socket -> Int -> IO ByteArray
typed :: ByteArray -> PrimArray a
untyped :: PrimArray a -> ByteArray

For simplicity, all error-handling is omitted. With the type-directed interface, the server is implemented as:

server :: Socket -> IO a
server sckt = forever $ do
  totalByteArray <- receive sckt 2
  let totalPrimArray = typed totalByteArray :: PrimArray (Fixed 'LittleEndian Word16)
  let Fixed total = indexPrimArray totalPrimArray 0
  numberByteArray <- receive sckt (8 * fromIntegral @Word16 @Int total)
  let (sum,prod) = foldlPrimArray'
        (\(!sumN,!prodN) (Fixed n) -> (sumN + n, prodN * n))
        (0,1)
        (typed numberByteArray :: PrimArray (Fixed 'LittleEndian Word64))
  reply :: MutablePrimArray RealWorld (Fixed 'LittleEndian Word64) <- newPrimArray 2
  writePrimArray reply 0 (Fixed sum)
  writePrimArray reply 1 (Fixed prod)
  send sckt . untyped =<< unsafeFreezePrimArray reply

Not all of the explicit type annotations are needed, but they have been provided for additional clarity. As long as the user ensures that the typed primitive arrays use Fixed in their element types, the endianness conversions are guaranteed to be correct.

Types

data ByteOrder

Byte ordering.

Constructors

BigEndian

most-significant-byte occurs in lowest address.

LittleEndian

least-significant-byte occurs in lowest address.

Instances

Bounded ByteOrder

Since: base-4.11.0.0

Defined in GHC.ByteOrder

Methods

minBound :: ByteOrder

maxBound :: ByteOrder

Enum ByteOrder

Since: base-4.11.0.0

Defined in GHC.ByteOrder

Methods

succ :: ByteOrder -> ByteOrder

pred :: ByteOrder -> ByteOrder

toEnum :: Int -> ByteOrder

fromEnum :: ByteOrder -> Int

enumFrom :: ByteOrder -> [ByteOrder]

enumFromThen :: ByteOrder -> ByteOrder -> [ByteOrder]

enumFromTo :: ByteOrder -> ByteOrder -> [ByteOrder]

enumFromThenTo :: ByteOrder -> ByteOrder -> ByteOrder -> [ByteOrder]

Eq ByteOrder

Since: base-4.11.0.0

Defined in GHC.ByteOrder

Methods

(==) :: ByteOrder -> ByteOrder -> Bool

(/=) :: ByteOrder -> ByteOrder -> Bool

Ord ByteOrder

Since: base-4.11.0.0

Defined in GHC.ByteOrder

Methods

compare :: ByteOrder -> ByteOrder -> Ordering

(<) :: ByteOrder -> ByteOrder -> Bool

(<=) :: ByteOrder -> ByteOrder -> Bool

(>) :: ByteOrder -> ByteOrder -> Bool

(>=) :: ByteOrder -> ByteOrder -> Bool

max :: ByteOrder -> ByteOrder -> ByteOrder

min :: ByteOrder -> ByteOrder -> ByteOrder

Read ByteOrder

Since: base-4.11.0.0

Defined in GHC.ByteOrder

Methods

readsPrec :: Int -> ReadS ByteOrder

readList :: ReadS [ByteOrder]

readPrec :: ReadPrec ByteOrder

readListPrec :: ReadPrec [ByteOrder]

Show ByteOrder

Since: base-4.11.0.0

Defined in GHC.ByteOrder

Methods

showsPrec :: Int -> ByteOrder -> ShowS

show :: ByteOrder -> String

showList :: [ByteOrder] -> ShowS

newtype Fixed :: ByteOrder -> Type -> Type where

A word whose byte order is specified (not platform dependent) when working with Prim and Storable.

Constructors

Fixed :: a -> Fixed b a

Instances

(FixedOrdering b, Prim a, Bytes a) => Prim (Fixed b a)

Defined in System.ByteOrder.Unsafe

Methods

sizeOf# :: Fixed b a -> Int#

alignment# :: Fixed b a -> Int#

indexByteArray# :: ByteArray# -> Int# -> Fixed b a

readByteArray# :: MutableByteArray# s -> Int# -> State# s -> (#State# s, Fixed b a#)

writeByteArray# :: MutableByteArray# s -> Int# -> Fixed b a -> State# s -> State# s

setByteArray# :: MutableByteArray# s -> Int# -> Int# -> Fixed b a -> State# s -> State# s

indexOffAddr# :: Addr# -> Int# -> Fixed b a

readOffAddr# :: Addr# -> Int# -> State# s -> (#State# s, Fixed b a#)

writeOffAddr# :: Addr# -> Int# -> Fixed b a -> State# s -> State# s

setOffAddr# :: Addr# -> Int# -> Int# -> Fixed b a -> State# s -> State# s

System Byte Order

targetByteOrder :: ByteOrder

The byte ordering of the target machine.

Classes

class Bytes a

Types that are represented as a fixed-sized word. For these types, the bytes can be swapped. The instances of this class use byteswapping primitives and compile-time knowledge of native endianness to provide portable endianness conversion functions.

Minimal complete definition

toBigEndian, toLittleEndian

Instances

Bytes Int8

Defined in System.ByteOrder.Class

Methods

toBigEndian :: Int8 -> Int8

toLittleEndian :: Int8 -> Int8

Bytes Int16

Defined in System.ByteOrder.Class

Methods

toBigEndian :: Int16 -> Int16

toLittleEndian :: Int16 -> Int16

Bytes Int32

Defined in System.ByteOrder.Class

Methods

toBigEndian :: Int32 -> Int32

toLittleEndian :: Int32 -> Int32

Bytes Int64

Defined in System.ByteOrder.Class

Methods

toBigEndian :: Int64 -> Int64

toLittleEndian :: Int64 -> Int64

Bytes Word8

Defined in System.ByteOrder.Class

Methods

toBigEndian :: Word8 -> Word8

toLittleEndian :: Word8 -> Word8

Bytes Word16

Defined in System.ByteOrder.Class

Methods

toBigEndian :: Word16 -> Word16

toLittleEndian :: Word16 -> Word16

Bytes Word32

Defined in System.ByteOrder.Class

Methods

toBigEndian :: Word32 -> Word32

toLittleEndian :: Word32 -> Word32

Bytes Word64

Defined in System.ByteOrder.Class

Methods

toBigEndian :: Word64 -> Word64

toLittleEndian :: Word64 -> Word64

class FixedOrdering (b :: ByteOrder)

A byte order that can be interpreted as a conversion function. This class is effectively closed. The only instances are for BigEndian and LittleEndian. It is not possible to write more instances since there are no other inhabitants of ByteOrder.

Minimal complete definition

toFixedEndian

Instances

FixedOrdering LittleEndian

Defined in System.ByteOrder.Unsafe

Methods

toFixedEndian :: Bytes a => a -> a

FixedOrdering BigEndian

Defined in System.ByteOrder.Unsafe

Methods

toFixedEndian :: Bytes a => a -> a

Convert

toBigEndian :: Bytes a => a -> a

Convert from a native-endian word to a big-endian word.

toLittleEndian :: Bytes a => a -> a

Convert from a native-endian word to a little-endian word.

fromBigEndian :: Bytes a => a -> a

Convert from a big-endian word to a native-endian word.

fromLittleEndian :: Bytes a => a -> a

Convert from a little-endian word to a native-endian word.